Effect of Minimally Invasive Extracorporeal Circulation on Optic Nerve Sheath Diameter and Stroke Incidence in Isolated Open Heart Surgery

Cardiopulmonary bypass (CPB)-associated neurological complications remain a significant concern in cardiac surgery, with stroke incidence ranging from 1.3% to 3.6% depending on procedure type, patient age, and comorbidities. The underlying mechanism involves cerebral embolism, hypoperfusion, and ischemia-reperfusion injury, with microemboli and hypoperfusion acting synergistically to impair cerebral washout - particularly in watershed regions.Minimally Invasive Extracorporeal Circulation (MiECC) systems were developed to improve biocompatibility, minimize adverse effects, and enhance end-organ protection compared to conventional CPB. MiECC utilizes a closed-circuit system with no venous reservoir, heparin-coated tubing, kinetic-assisted venous drainage, and a minimal prime volume (~500-700 mL), which significantly improves microcirculation and renders cardiac surgery more physiological.Optic nerve sheath diameter (ONSD), measured by ultrasound, provides a non-invasive, objective, and reproducible method for assessing intracranial pressure (ICP). The optic nerve sheath communicates with the subarachnoid space and dilates in response to elevated ICP. An ONSD exceeding 5.35 mm has been shown to correlate strongly with ICP above 20 mmHg on CT measurement.

In this prospective randomized controlled trial, adult patients undergoing elective isolated open heart surgery will be randomized into two groups: MiECC (n=50) and conventional CPB (n=50). Anesthesia will be standardized across both groups. ONSD will be measured bilaterally at 7 predefined time points (T0: preoperative baseline; T1: 15 min after CPB onset; T2: mid-CPB during cross-clamp; T3: before CPB weaning; T4: 30 min post-CPB; T5: postoperative hour 6; T6: postoperative hour 24) using a high-frequency linear probe (7.5-10 MHz), with measurements taken 3 mm behind the optic disc. Cerebral oxygenation will be monitored by NIRS.Neurological assessment will include full neurological examination, MoCA testing (preoperative, postoperative day 7 and 30), CAM-ICU delirium scoring (daily in ICU), and brain CT/MRI in case of suspected stroke. Stroke is defined as focal or global neurological deficit lasting more than 24 hours, confirmed by neuroimaging and graded by NIHSS.

The study aims to determine whether MiECC reduces perioperative intracranial pressure elevation (as reflected by ONSD) and postoperative stroke incidence compared to conventional CPB, and to evaluate the utility of ONSD as a routine non-invasive stroke predictor in open heart surgery.

Inclusion criteria

• Age 18 to 80 years
• Scheduled for elective isolated open heart surgery
• Requires cardiopulmonary bypass
• Able to provide written informed consent
• Adequate ultrasonographic window for ONSD measurement

Exclusion criteria

• Emergency or salvage surgery
• Off-pump, revision, or combined cardiac surgery
• History of stroke or TIA within the last 6 months
• Pre-existing neurological deficit
• Bilateral optic nerve pathology
• History of ocular trauma or surgery
• Intracranial mass or hydrocephalus
• Requirement for deep hypothermic circulatory arrest
• Alcohol or substance dependency
• Left ventricular ejection fraction <30%
• Renal or hepatic failure with risk of advanced encephalopathy
• Preoperative requirement for mechanical circulatory support
• Symptomatic or severe carotid artery stenosis (>70%)
• Refusal to participate in the study